1. Field of the Invention
The present invention relates to a postprocessing apparatus (also called a finisher) which subjects a sheet where an image is formed by an image forming apparatus such as a copying machine, a printer, a facsimile apparatus, or a composite machine of them, to a punching process, a two-fold process, a Z-fold process, a stitching process, and the like, and an image forming system which has this postprocessing apparatus.
2. Description of Related Art
In recent years, there have been provided a postprocessing apparatus which subjects a sheet where an image is formed by an image forming apparatus such as a copying machine, a facsimile apparatus, or a composite machine of them, to a punching process, a two-fold process, and a Z-fold process, to enable file stitching, and an image forming system which is obtained by adding an image forming apparatus to this postprocessing apparatus.
A postprocessing apparatus which subjects a bundle of sheets, that form one set with a plurality of sheets, to a saddle stitching process is disclosed in Japanese Unexamined Patent Publication Nos. 6-72064, 7-187479, 8-192951, and the like.
A postprocessing apparatus which enables center folding is proposed in Japanese Unexamined Patent Publication Nos. 7-48062, 10-148983, 10-167562, and 11-348451, U.S. Pat. No. 5,108,082, and the like.
A processing apparatus which subjects a sheet to a folding process is popular in the field of bookbinding. A processing apparatus which folds one or a comparatively small number of sheets is popular as an apparatus for forming a sealed document such as a postal matter.
A punching apparatus described in Japanese Unexamined Patent Publication No. 6-182697 is provided midway along the sheet convey path of a sorter that sorts sheets delivered from an image forming apparatus.
A bookbinding apparatus described in Japanese Unexamined Patent Publication No. 8-319054 has a punching means for forming string binding holes in a sheet by a punching process. The punching means is provided midway along the sheet convey path of the bookbinding apparatus which binds a plurality of sheets, delivered from the delivery portion of a copying machine, in a stacked state.
A folding apparatus for subjecting a sheet to a folding process such as a Z-fold process or the like is disclosed in Japanese Unexamined Utility Model Publication No. 62-68973, Japanese Unexamined Patent Publication No. 4-64577, and the like.
A sheet postprocessing apparatus which enables folding in two is disclosed in Japanese Unexamined Patent Publication Nos. 10-148983 and 10-167562.
Any conventional folding apparatus is a large, expensive one which aims at processing a large number of sheets at a high speed.
In addition to a large number of uniform documents, many documents need to be handled differently in a comparatively small unit. Among documents to be sealed such as direct mail, documents which bear different information such as addresses, e.g., slips, need folding. In this case, the different documents must be manually sorted before or after they are subjected to a folding apparatus.
In this manner, the conventional apparatus which uniformly processes a large number of documents cannot improve the overall efficiency.
The conventional postprocessing apparatus has a center folding portion and three-fold portion that are separate from each other, to complicate the structure that forms different sheet convey paths. Particularly in a structure in which the different sheet convey paths are bent, jamming tends to occur easily.
Furthermore, in the conventional postprocessing apparatus which performs punching, folding into a Z shape, and folding in two, punching is performed after an image recording sheet delivered from an image forming apparatus is folded. The fold of a folded sheet is not always parallel to the leading end or trailing end of the sheet in the convey direction, but is sometimes skew from it. If the skew sheet is punched with reference to its fold for abutment, holes are not formed at predetermined positions of the sheet. When sheets each punched in this manner are filed, a plurality of sheets become unaligned.